What is an asteroid? Imagine a potato 5km long and 2km wide hurling though space like a badly thrown football. Now imagine that spud crashing into your backyard and decimating the planet with the combined energy of millions of atomic bombs.

Such a collision would destroy most of life on Earth. Any surviving cockroaches would be mighty pleased, however.

Enter Asteroid PHA 4179

"The space spud is PHA (Potentially Hazardous Asteroid) 4179. French scientists discovered the asteroid in 1989 and named it Toutatis after the Gaulish god of Thunder and Destruction. Toutatis' peculiar shape, wobbly rotation and wacky orbit make it unique among the near-Earth asteroids whizzing around our blue planet. Scientists at NASA's Jet Propulsion Laboratory in Pasadena, Calif., study these space rocks with radar. [. . .]

"Orbit-altering experiences with planets Earth, Mars, Venus and Jupiter, as well as the Sun, make Toutatis consistently inconsistent, passing closer or farther to larger bodies as gravity wills. On its most recent visit, October 31, 2000, Toutatis passed within less than 29 lunar distances of earth (a lunar distance is the average distance from Earth to Moon: 384,400 km). When Toutatis is next in the neighborhood (galactically speaking), on Sept. 29, 2004, it will pass just 4 lunar distances from Earth.

The asteroid will be the brightest it's ever been and easy to see through binoculars."

The concept of a large meteor like this one eventually breaking through our atmosphere and trashing the Earth is hardly just Hollywood fluff. It's been surmised by several scientists that an asteroid just like Toutatis struck what is now Mexico about 65 million years ago and effectively ended the dinosaur age in one fell swoop.

Asteroids and Near Earth Orbits

Nor is this a mere tale of bygone days. On March 23, 1989, an asteroid with a kinetic energy of over 1000 one-megaton hydrogen bombs (i.e., about 5,000 times more powerful than the bomb dropped on Hiroshima) was recorded to have passed very close to Earth. Named 1989FC, scientists only discovered the closeness of its pass to the Earth after the fact, during a calculation of the asteroid's entire orbital path.

Then in 1994, the new Spacewatch Camera in Arizona discovered four asteroids that sped by twice as close to us as our nearest neighbor, the Moon.

News of these activities brought what are called Near Earth Objects (NEOs) into the political arena.

What--if anything--are scientists and governments doing about this? Is it that much of a concern, or were those close passes simply freakish accidents, horrible things that--thankfully--almost never happen?

Asteroids Are Like Comets

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Asteroids, like comets, are really just chunks of flying debris left over from the formation of the solar system about 4.5 billion years ago. Some are huge; for instance, the potato-shaped asteroid Eros is bigger than the whole District of Colombia.

Before you freak out entirely, it must be noted here that the statistics on the chances of an NEO over one kilometer (3,000 feet) long--about the size of the one that probably killed off the dinosaurs--hitting the Earth soon are practically nil. A hit by such an asteroid is unlikely to hit Earth for hundreds of thousands of years. By then we're probably sure to have something to at least alter the NEO's course . . . if we're still around, that is.

And because many asteroids heading for us end up bouncing off our atmosphere or principally burning up on entry, there aren't many asteroids that can get through and maintain the size necessary to cause widespread damage.

The statistics on smaller hits are vague and subject to change, however. In the general press, too little coverage is given to the small asteroids which could conceivably cause terrible local destruction (e.g., to nearby coastal cities) but little worldwide impact, and which probably hit once every hundred years.

Also, our current best telescopes can hardly see the 100-meter asteroids because they're so small; hence the vague statistics.

Still, "Near Earth Objects"--the term "near" is a pretty relative one, since it refers to space debris within a third of the distance to the sun--pose a threat to all nations.

For instance, a reasonably large asteroid of 200 meters (600 feet) in diameter crashing into the Atlantic Ocean could create a tsunami (a giant tidal wave) that would sink both Britain and the entire East Coast of the United States within minutes.

Up to the 1970s, there was actually little interest in asteroids, including NEOs. They were considered little more than low class astronomical objects. Indeed, the small comet which destroyed hundreds of square kilometers in remote Siberia in 1908 was an event little known to the general public.

And a small asteroid which skimmed the upper atmosphere in the 1970s, as detected by a US military satellite, received little publicity.

Things began to change in the late 70s. A small but increasing number of astronomers interested in asteroids began to be concerned by the abundance of these objects passing close to the Earth. They instituted processes to catalog the asteroids accidentally seen on telescopic plates that had not previously been recorded.

Theoretical computer models revealed that the gravity of the planets caused a sizable number of asteroids from the Main Belt between Mars and Jupiter to cascade down into lower orbits, with many approaching the Earth. Further, a significant fraction of comets passing through the inner solar system would be diverted into orbits near Earth, due to gravitational encounters with the inner planets.

As a result of these discoveries, the estimated number of NEOs expanded by about 1000 times.

After that, some in the know say half-jokingly, even scientists and government officials began taking notice.

New telescope technology (CCDs) emerging around 1990 increased the discovery rate of all asteroids and eventually confirmed their abundance via solid statistical sampling rates. In fact, it is now estimated that there are about 300,000 Near-Earth Asteroids over 100 meters (about 300 feet) in diameter, and about 2,000 over 1 kilometer (3,000 feet) in diameter.

What does that mean to us? Well, if an asteroid at least 1 kilometer in size hit Earth, it would cause a dust cloud which would block out sunlight for at least a year and lead to a deep worldwide winter, exhausting food supplies. The latter is what caused the dinosaur extinction.

Many scientists estimate the impact by a single 1-km object could kill up to a quarter of our planet's population.

Smaller hits--about 100-200-meters (300-600 feet), say--are far more common. Unfortunately for research, their effect doesn't show up much in global geologic histories. It is estimated, however, that such hits have created many local tsunamis and brief climate changes in recorded history, without any understanding of their cause at the time.

Cruel, Cruel Fate

Luckily, Earth's atmosphere gives protection against the vast majority of small asteroids. Asteroids hit the atmosphere at typical speeds in excess of 10 km/sec. Those whose entire orbits reside within the inner solar system hit with an average of about 20 km/sec - with exact relative speed depending upon their angle of approach - and with speeds over 50 km/sec common for small cometary objects making a pass from the outer solar system.

At this speed, they usually break up due to severe shock pressures, and burn up due to friction with the atmosphere. Think about it -- 10 kilometers per second (6 miles per second) is bone-scrapingly fast -- about 36,000 kilometers (22,000 miles) per hour.

For asteroids coming in at 20 km/sec, it's generally thought that to penetrate the atmosphere and cause major damage by tsunami, an iron asteroid must be around 40 to 60 meters in diameter, and a stony asteroid 200 meters in diameter.

However, a stony asteroid 60 meters in diameter can cause significant damage by explosion due to atmospheric influence.

The exact damage inflicted by an asteroid or comet depends upon a number of factors -- size, speed, composition of object, and whether it hits land or ocean.

For a land impact, it can be said that an object of roughly 75 meters (225 feet) diameter can probably destroy a city, a 160-meter (480-foot) object can destroy a large urban area, a 350-meter (1050-foot) object can destroy a small state, and a 700-meter (2,100-foot) object can destroy a small country.

Smaller objects can cause far more widespread damage with an ocean impact. The effects of an ocean impact are felt much further away than the effects of an air burst due to the more effective generation of water waves, and the fact that human populations and assets are largely concentrated in coastal cities.

For example, the earthquake-induced tsunami in Chile in 1960 produced waves in Hawaii 10,600 km away of height up to over 10 meters (30 feet), and up to 5 meters (15 feet) in Japan 17,000 km away with an average of 2 meters, causing heavy damages and loss of lives.

The damage caused by a tsunami is due not just by a heavy wall of water hitting things, but much more to the solid debris carried by the powerful, churning deep water wave as it hits the continental shelf--the solid debris rams and batters anything in its way.

The 1998 earthquake-induced tsunami in Papua New Guinea that wiped out coastal villages and killed uncounted thousands of people was only a few meters high.

If an asteroid hit the ocean, we could see a tsunami wave 100 times higher.

Such a tsunami would cause unprecedented damage to now-developed low lying areas all along the U.S. east coast, and may totally submerge vast areas in Europe such as Holland and Denmark. A 100-meter (300-foot) tsunami would travel inland about 22 km (14 miles) and a 200 meter (600-foot) tsunami would travel inland about 55 km (34 miles).

How to Deflect an Asteroid

There simply is no good way to fight or run away from a killer asteroid. So what can we do?

The trick to stopping a killer asteroid will be early, early detection, and quick, effective interplanetary action by the world's governments.

Fine, but how can this be done? The Task Force on Potentially Hazardous Near Earth Objects writes:

"A number of possible mechanisms have been considered for deflecting or breaking up potentially hazardous Near Earth Objects; most would require the use of a spacecraft with some means of transferring energy or momentum to the object, for example by kinetic energy transfer (by heavy projectiles carried on the spacecraft or by causing a collision between asteroids), by chemical or nuclear explosives, or even by mounting "sails" on the object to harness the Sun's radiation pressure.

"Some of these mechanisms are more realistic than others. [. . .]

"To try to destroy an asteroid or comet in space by a single explosive charge on or below its surface would risk breaking it uncontrollably into a number of large pieces which could still hit the Earth, doing even more damage.

"A more promising method would be to fly a spacecraft alongside the object, perhaps for months or years, nudging it in a controlled way from time to time with explosives or other means.

"This relatively gentle approach is particularly important because many asteroids and comets are held together only by their own very weak gravitational fields. The longer the time before impact, the more effective even a small nudge would be."

There have been many scientific analyses on alternate ways to deal with a large object on a collision course with Earth.

The methods can be roughly split into two categories -- destruction and deflection.

Destruction means breaking up the object into pieces small enough that none can penetrate the Earth's atmosphere. For example, if done by nuclear detonation, the dispersion of the fragments would mean that most--but not all--pieces would miss the Earth.

The further away the detonation, the more dispersed the pieces by the time they arrive in Earth's vicinity. As you can see, blowing up the object is actually a combination of destruction and deflection -- the dispersion is a sort of deflection. The problem with destruction is the uncertainty of explosions. Success is risky.

Deflection means simply nudging the body so that it misses the Earth.

The further away the object is from Earth, the less we need to nudge it because the change in its trajectory adds up over time.

If we detect an object on an impact trajectory, then we will need to make a decision on a method of planetary defense. The method chosen will depend upon the size of the object, how soon we can rendezvous with it, of what the object consists, the rotation rate of the object, its geometry, and any fractures in the object.

There would be considerable uncertainty regarding the composition of the object without a thorough on-site visit. For analysis purposes at this point in time, models have considered objects consisting primarily of ice, friable material, gravel, hard rock and pure metal.

Most proposed methods have been rejected due to risk and economic and/or technical feasibility in the near future. The remaining methods seriously considered to date include:

1.) Blowing it up with a nuclear bomb -- This option is generally unfavored because it seems unlikely that it would completely break up most objects well enough, or assuredly move all pieces into a non-impact trajectory.

It's still considered because it is economical and technically feasible -- it might work, and it might be all we can do if given extremely short notice.

2.) Nudging it by nuclear bomb -- This option detonates a nuclear bomb above the surface of a volatile asteroid or comet, causing intense heat at the surface in order to create gas jets which would thrust it away from Earth.

Another nuclear nudge option is to blow off a piece by targeting an existing natural fizzure, splitting it in two so that both dangerous pieces miss the Earth in a straddling way.

The drawback to both options is that both are often considered too 'slick' for scientists to be certain of their results. However, it very well might work, and it might be the most reasonable option if given very short notice.

3.) Nudging it by kinetic impact--This option simply has a sizable object strike the asteroid or comet at high speed in order to nudge it, possibly with an explosion upon impact to enhance the effect. This could work with small objects. The risk is that it will fragment the target and put a sizable chunk on a collision course with Earth.

4.) Thrusting the object--This precludes utilizing something on the asteroid that can be used to propel the object from its current trajectory. This option is attractive for very small objects whereby it would be feasible to send up to the asteroid a very high performance engine with the required fuel propellant for the move; for small to medium sized objects known to be rich in water, we could use it as fuel propellant in a thermal rocket.

Nuclear rockets (which use a small nuclear reactor to heat any kind of propellant) would be preferred for their simplicity and high performance.

Notably, solar ovens would not be preferred in the immediate future compared to a nuclear thermal rocket. Lack of simplicity, uneven performance, and the possible need to clean dirty mirrors argue against the solar device.

The advantage of thrusting is that the object won't be fragmented, giving us more control. The disadvantage is that it won't handle very large objects in a short time frame.

If an object were approaching Earth and we were given sufficient time, we could send out multiple missions using different techniques. If the first mission failed, a second mission could give it a shot. If an earlier mission fragments the asteroid, a later mission could deal with a fragment on a collision course with Earth. If it's a large object, it could fragment into multiple threats.

But in all cases, the more advanced notice we have, the greater our chances for success. The experts agree that time is the critical element which can make all the difference in the world.

Tips for Surviving an Asteroid Impact

Surviving an Extinction Event Not Likely

Large asteroids are likely to lead to extinction events -- the damage will be so catastrophic that most life on earth will simply perish. There's no sense in trying to prepare to survive something to this extent -- not unless you're a government that has a lot of money to spend and can afford to build large, self-sustaining "bio-dome" bunkers deep underground and away from the point of impact.

Then whoever lives in these underground "bio-domes" (perhaps small communities of people) would need to be prepared to stay underground for several years, perhaps relying on data from satellites in space as to what condition were now like on earth after the impact.

Temperatures will have dropped significantly around the planet, bringing in a new ice age, while killing most life on earth. As the years pass and the climate begins to change to safer levels once again for life, these people still alive deep underground could one day emerge to a completely different planet, and begin the painstaking task of re-populating the earth with whatever "life" they had managed to keep with them deep underground.

Better Odds: Surviving the Impact of a Smaller Asteroid

While most people on earth would perish as the result of an asteroid impact of this size, what about a smaller asteroid?

Since these are a lot more likely to take place, due to the large number of meteors in our solar system, we have a much better chance of surviving, especially if we don't live anywhere near the impact or along the coast (should it strike in a nearby ocean).

To get an idea of how to survive, treat an asteroid impact a lot like a combination of a nuclear bomb (minus the fallout), catastrophic earthquake, and tsunami -- all rolled into one.

Underground "Cold War" style bunkers would allow for families to seek shelter prior to an impact. For example, if NASA told us we had a few days until an asteroid strike (or possible strike), a person could hide-out in their bunker, ready to stay down there for several days, should an asteroid strike nearby.

For the majority who choose not to build a "Cold War" style bunker and instead chance the impact, it would be recommended that they head inland and to a higher elevation, in the days leading up to the asteroid collision. If the asteroid lands in the ocean, coastal regions (on continents on both sides of the ocean) are going to be flooded by a mega-tsunami.

Evacuation: Key to Surviving an Asteroid Collision

Plan for this event a lot like you would plan for the likelihood of a nuclear war. Have a secondary location (perhaps a cabin in the mountains or a friend or relative in a distant small town) that you can evacuate to.

Since this is an asteroid you're planning an evacuation for, and not a nuclear terrorist attack, you can first attempt to evacuate by car; hopefully state official will begin evacuations days in advance so that major cities being evacuated aren't paralyzed by millions of fleeing residents.

Keep survival supplies on hand that you can pack in the trunk of your car, even on the roof of your car, and if possible also in a pull-behind trailer (such as extra gasoline, considering that gas stations may be empty of gas after a massive run for fuel by hundreds of thousands of people).

Pack a mountain bike for each member of your family, as well as a backpack that each person can carry on their back while riding a bike. Also consider "tow-behind" bicycle trailers for carrying goods. If for some reason you have to abandon your car, these mountain bikes will provide a secondary means of transportation. Or of course you can just hoof it on foot, which might be best anyway, as you'll be able to carry more supplies with you (unless you've got that tow-behind trailer for your bikes).

A small asteroid impact will cause catastrophic damage, but it will be more localized, effecting a much smaller area than an "extinction event" causing asteroid.

After an evacuation, if an asteroid hits near the city that you've fled from, you may have no home or community to return to in the coming months, if it has been completely wiped off the map by the asteroid.

In that case, you're technically a refugee.

If you have relatives or friends in distant places you haven't talked to in years, consider warming up those relationships. Call and say hello more than once a year.

The more people who you know (and who like you) in distant places, the more possible locations you have for beginning a new life, should your home town ever be completely destroyed by an asteroid and you have to evacuate.

It's either warm up those relationships with distant relatives or look forward to life in a FEMA Camp with a few hundred thousand other refugees who've also fled the region.